Dimeric unsaturated aldehydes could be very useful in many applications if they could be produced economically. Dimeric unsaturated aldehydes can be used as a starting material for many useful products. One group of products are glycols that can be used for the preparation of polyesters. The resulting glycols are flexible and can be produced by reducing the dimeric unsaturated aldehydes. The polyesters produced from glycols with large aliphatic side groups produce flexible polymers with low glass transition temperatures. Flexible glycols and glycols with large side chains act as their own plasticizing agent when incorporated into a polyester.
Dimeric unsaturated aldehydes could also find a use in the production of polyurethanes and nylons by reductive amination to produce flexible diamine monomers.
The dimeric unsaturated aldehydes are also useful for preparing diacrylates or dicarboxylates. The diacrylates could function as property modifiers for acrylic resins. The dicarboxylates could be used as the diacid component of polyester.
Although dimeric unsaturated aldehydes could find uses in many applications their production is relatively costly, thus limiting their current use. Dimeric unsaturated aldehydes are generally prepared by condensing an allylically halogenated aldehyde with the corresponding allylic unsaturated aldehyde carbanion. However, allylically halogenating the unsaturated aldehyde and making the unsaturated aldeyde carbanion are both very costly, and furthermore combining these two intermediates produce the desired product plus a stoichiometric amount of salt, the disposal of which is difficult. Another method of producing dimeric unsaturated aldehydes entails the dehydrohalogenation of dihalodihalides, which in turn come from the hydrofomylation of divinyldihalides. As with the above process, this process is expensive and produces salt.
It would be very desirable to be able to produce dimeric unsaturated aldehydes from an inexpensive starting material at high yields and high conversion by an inexpensive process avoiding the high cost and pollution problems of the prior art.
It is known that copper catalysts form ketones from conjugated unsaturated aldehydes containing methylene groups (Rec. Trav. Chim., 84, 1203 (1965). Copper catalysts are also known to oxidatively cleave electron rich aromatic phenols and amines to muconic acid (Tetr., 34, 641 (1978). Copper, pyridine catalysts are also known to effect the oxidative coupling of terminal alkynes (Org. Snyth. Coll. Vol. V, 517 (1973) and J. Amer. Chem. Soc., 99, 1487 (1977).
It is also known that the coupling of ketones with copper catalyst requires extensive substitution with cyano and aromatic groups to stabilize the intermediate oxidation product (J. Org. Chem., 36, 3160, (1971). It is known that homoconjugated unsaturated ketones are oxidatively coupled with copper, pyridine, methanol catalyst (Rec. Trav. Chim., 84, 1233 (1965).